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.TH EXPR 1 "Aug 29, 2003"
.SH NAME
expr \- evaluate arguments as an expression
.SH SYNOPSIS
.LP
.nf
\fB/usr/bin/expr\fR \fIargument\fR...
.fi

.LP
.nf
\fB/usr/xpg4/bin/expr\fR \fIargument\fR...
.fi

.LP
.nf
\fB/usr/xpg6/bin/expr\fR \fIargument\fR...
.fi

.SH DESCRIPTION
.SS "/usr/bin/expr, /usr/xpg4/bin/expr"
.sp
.LP
The \fBexpr\fR utility evaluates the expression and writes the result to
standard output. The character \fB0\fR is written to indicate a zero value and
nothing is written to indicate a null string.
.SS "/usr/xpg6/bin/expr"
.sp
.LP
The \fBexpr\fR utility evaluates the expression and writes the result to
standard output followed by a NEWLINE. If there is no result from \fBexpr\fR
processing, a NEWLINE is written to standard output.
.SH OPERANDS
.sp
.LP
The \fIargument\fR operand is evaluated as an expression. Terms of the
expression must be separated by blanks. Characters special to the shell must be
escaped (see \fBsh\fR(1)). Strings containing blanks or other special
characters should be quoted. The length of the expression is limited to
\fBLINE_MAX\fR (2048 characters).
.sp
.LP
The operators and keywords are listed below. The list is in order of increasing
precedence, with equal precedence operators grouped within \fB{\|}\fR symbols.
All of the operators are left-associative.
.sp
.ne 2
.na
\fB\fIexpr\fR \fB\e|\fR \fIexpr\fR\fR
.ad
.sp .6
.RS 4n
Returns the evaluation of the first \fIexpr\fR if it is neither \fINULL\fR nor
\fB0\fR; otherwise, returns the evaluation of the second \fIexpr\fR if it is
not \fINULL\fR; otherwise, \fB0\fR.
.RE

.sp
.ne 2
.na
\fB\fIexpr\fR \fB\e&\fR \fIexpr\fR\fR
.ad
.sp .6
.RS 4n
Returns the first \fIexpr\fR if neither \fIexpr\fR is \fINULL\fR or \fB0\fR,
otherwise returns \fB0\fR.
.RE

.sp
.ne 2
.na
\fB\fIexpr\fR{ \fB=\fR, \fB\e>\fR, \fB\e>=\fR, \fB\e<\fR, \fB\e<=\fR, \fB!=\fR}
\fIexpr\fR\fR
.ad
.sp .6
.RS 4n
Returns the result of an integer comparison if both arguments are integers,
otherwise returns the result of a string comparison using the locale-specific
coalition sequence. The result of each comparison will be \fB1\fR if the
specified relationship is \fBTRUE\fR, \fB0\fR if the relationship is
\fBFALSE\fR.
.RE

.sp
.ne 2
.na
\fB\fIexpr \fR{ \fB+\fR, \fB\(mi \fR} \fIexpr\fR\fR
.ad
.sp .6
.RS 4n
Addition or subtraction of integer-valued arguments.
.RE

.sp
.ne 2
.na
\fB\fIexpr \fR{ \fB\e*\fR, \fB/\fR, \fB%\fR} \fIexpr\fR\fR
.ad
.sp .6
.RS 4n
Multiplication, division, or remainder of the integer-valued arguments.
.RE

.sp
.ne 2
.na
\fB\fIexpr\fR \fB:\fR \fIexpr\fR\fR
.ad
.sp .6
.RS 4n
The matching operator \fB:\fR (colon) compares the first argument with the
second argument, which must be an internationalized basic regular expression
(BRE), except that all patterns are anchored to the beginning of the string.
That is, only sequences starting at the first character of a string are matched
by the regular expression. See \fBregex\fR(7) and NOTES. Normally, the
\fB/usr/bin/expr\fR matching operator returns the number of bytes matched and
the \fB/usr/xpg4/bin/expr\fR matching operator returns the number of characters
matched (\fB0\fR on failure). If the second argument contains at least one BRE
sub-expression [\e(...\e)], the matching operator returns the string
corresponding to \e1.
.RE

.sp
.ne 2
.na
\fB\fIinteger\fR \fR
.ad
.sp .6
.RS 4n
An argument consisting only of an (optional) unary minus followed by digits.
.RE

.sp
.ne 2
.na
\fB\fIstring\fR \fR
.ad
.sp .6
.RS 4n
A string argument that cannot be identified as an \fIinteger\fR argument or as
one of the expression operator symbols.
.RE

.SS "Compatibility Operators (x86 only)"
.sp
.LP
The following operators are included for compatibility with INTERACTIVE UNIX
System only and are not intended to be used by non- INTERACTIVE UNIX System
scripts:
.sp
.ne 2
.na
\fB\fBindex\fR \fIstring character-list\fR\fR
.ad
.sp .6
.RS 4n
Report the first position in which any one of the bytes in \fIcharacter-list\fR
matches a byte in \fIstring\fR.
.RE

.sp
.ne 2
.na
\fB\fBlength\fR \fIstring\fR\fR
.ad
.sp .6
.RS 4n
Return the length (that is, the number of bytes) of \fIstring\fR.
.RE

.sp
.ne 2
.na
\fB\fBsubstr\fR \fIstring integer-1 integer-2\fR\fR
.ad
.sp .6
.RS 4n
Extract the substring of \fIstring\fR starting at position \fIinteger-1\fR and
of length \fIinteger-2\fR bytes.  If \fIinteger-1\fR has a value greater than
the number of bytes in \fIstring\fR, \fBexpr\fR returns a null string.  If you
try to extract more bytes than there are in string, \fBexpr\fR returns all the
remaining bytes from \fIstring\fR. Results are unspecified if either
\fIinteger-1\fR or \fIinteger-2\fR is a negative value.
.RE

.SH EXAMPLES
.LP
\fBExample 1 \fRAdding an integer to a shell variable
.sp
.LP
Add 1 to the shell variable \fBa\fR:

.sp
.in +2
.nf
example$ \fBa=`expr\| $a\| +\| 1`\fR
.fi
.in -2
.sp

.LP
\fBExample 2 \fRReturning a path name segment
.sp
.LP
The following example emulates \fBbasename\fR(1), returning the last segment of
the path name \fB$a\fR. For \fB$a\fR equal to either \fB/usr/abc/file\fR or
just \fBfile\fR, the example returns \fBfile\fR. (Watch out for \fB/\fR alone
as an argument: \fBexpr\fR takes it as the division operator. See NOTES below.)

.sp
.in +2
.nf
example$ \fBexpr $a : '.*/\e(.*\e)' \e| $a\fR
.fi
.in -2
.sp

.LP
\fBExample 3 \fRUsing // characters to simplify the expression
.sp
.LP
Here is a better version of the previous example. The addition of the \fB//\fR
characters eliminates any ambiguity about the division operator and simplifies
the whole expression.

.sp
.in +2
.nf
example$ \fBexpr //$a : '.*/\e(.*\e)'\fR
.fi
.in -2
.sp

.SS "/usr/bin/expr"
.LP
\fBExample 4 \fRReturning the number of bytes in a variable
.sp
.in +2
.nf
example$ \fBexpr "$VAR" : '.*'\fR
.fi
.in -2
.sp

.SS "/usr/xpg4/bin/expr"
.LP
\fBExample 5 \fRReturning the number of characters in a variable
.sp
.in +2
.nf
example$ \fBexpr "$VAR" : '.*'\fR
.fi
.in -2
.sp

.SH ENVIRONMENT VARIABLES
.sp
.LP
See \fBenviron\fR(7) for descriptions of the following environment variables
that affect the execution of \fBexpr\fR: \fBLANG\fR, \fBLC_ALL\fR,
\fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
.SH EXIT STATUS
.sp
.LP
As a side effect of expression evaluation, \fBexpr\fR returns the following
exit values:
.sp
.ne 2
.na
\fB\fB0\fR \fR
.ad
.RS 7n
If the expression is neither \fINULL\fR nor \fB0\fR.
.RE

.sp
.ne 2
.na
\fB\fB1\fR \fR
.ad
.RS 7n
If the expression is either \fINULL\fR or \fB0\fR.
.RE

.sp
.ne 2
.na
\fB\fB2\fR \fR
.ad
.RS 7n
For invalid expressions.
.RE

.sp
.ne 2
.na
\fB\fB>2\fR \fR
.ad
.RS 7n
An error occurred.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
CSI	enabled
_
Interface Stability	Standard
.TE

.SH SEE ALSO
.sp
.LP
.BR basename (1),
.BR ed (1),
.BR sh (1),
.BR Intro (3),
.BR attributes (7),
.BR environ (7),
.BR regex (7),
.BR standards (7)
.SH DIAGNOSTICS
.sp
.ne 2
.na
\fB\fBsyntax error\fR\fR
.ad
.RS 24n
Operator and operand errors.
.RE

.sp
.ne 2
.na
\fB\fBnon-numeric argument\fR\fR
.ad
.RS 24n
Arithmetic is attempted on such a string.
.RE

.SH NOTES
.sp
.LP
After argument processing by the shell, \fBexpr\fR cannot tell the difference
between an operator and an operand except by the value. If \fB$a\fR is an
\fB=\fR, the command:
.sp
.in +2
.nf
example$ \fBexpr $a = '='\fR
.fi
.in -2
.sp

.sp
.LP
looks like:
.sp
.in +2
.nf
example$ \fBexpr = = =\fR
.fi
.in -2
.sp

.sp
.LP
as the arguments are passed to \fBexpr\fR (and they are all taken as the
\fB=\fR operator). The following works:
.sp
.in +2
.nf
example$ \fBexpr X$a = X=\fR
.fi
.in -2
.sp

.SS "Regular Expressions"
.sp
.LP
Unlike some previous versions, \fBexpr\fR uses Internationalized Basic Regular
Expressions for all system-provided locales. Internationalized Regular
Expressions are explained on the \fBregex\fR(7) manual page.
